The present invention relates to a process for the treatment of waste water and gases containing organic sulphur compounds, by means of peroxide compounds such as hydrogen peroxide.
The sewage from public systems and certain types of industrial waste water contain evil-smelling and toxic organic sulphur compounds which can be responsible for colouring the water.
Thus, in the paper industry, during the digestion of the wood chips in the kraft process, organic sulphur compounds are formed, such as methylmercaptan, dimethyl sulphide and dimethyl disulphide, which are found again in the black liquors from digestion, the condensates from digestion, the wash water and the water from bleaching of the pulp.
The presence of these sulphur compounds in these effluents presents various problems. Thus, the calcination of the sludges obtained by concentration of the black liquors is accompanied by nauseating smells. Likewise, the condensates from digestion, the water from washing of the unbleached pulp resulting from digestion, and, if appropriate, the waste water from certain bleaching steps, cannot be discharged as such, because of their brownish colouration and their unpleasant smell.
To remove these organic sulphur compounds, it is known to subject them to oxidation, which leads to the formation of odourless and non-toxic compounds. Peroxide compounds have proved effective for this purpose. Thus, it has already been proposed to remove the organic sulphur compounds (mercaptans, dialkyl sulphides and dialkyl disulphides) present in certain waste gases, by treating them with an acid aqueous solution of hydrogen peroxide, in the presence of an iron catalyst (Interox, Effluent & Water Treatment Journal, August 1979). However, the treatments known hitherto do not make it possible to oxidise all the organic sulphur compounds quantitatively and to convert them totally to odourless products. More particularly, dialkyl disulphides are particularly resistant to complete oxidation, and the bad smells and the colourations for which these compounds are responsible cannot be removed completely by the known treatments.